Aerosol dispensers have been available for a number of years for the application of hair sprays and other personal care products, as well as for paints, lubricants, insecticides and a multitude of other liquid products.
In the earlier days of aerosol marketing, "Freon" blends were widely used as propellants, principally because they were not flammable and were relatively nontoxic. However, in recent years, it was discovered that "Freons," when released into the atmosphere, migrated to the upper stratosphere and contributed to the depletion of ozone. Since ozone shields the surface of the earth against penetration of solar ultraviolet radiation, the use of "Freon" propellants was believed by many to have contributed to climate changes, as well as to an increased incidence of skin cancers and cataracts. Accordingly, the U.S. Environmental Protection Agency (E.P.A.) banned the further use of "Freon" propellants. This forced aerosol packagers to select from alternative propellant systems, all of which had serious disadvantages. One class of propellants were the various hydrocarbons, consisting of blends of propane and butane mixtures. However, such hydrocarbon propellants are extremely flammable, and being volatile organic compounds they contribute to lower atmospheric air pollution. Therefore it is deemed desirable to reduce their usage from the conventional one part hydrocarbon propellant to three parts product on a weight basis. Two alternative propellant systems to hydrocarbons involve the use of hydrochlorofluorocarbons (HCFC's) and dimethylether. However, such propellants are extremely expensive and, in the case of dimethylether, flammable. Therefore a system which minimizes the amount of such propellants being utilized is deemed desirable.
In addition to the selection of a gas propellant, further problems in the aerosol packaging industry resides in the disposition of the used aerosol containers, particularly for large scale commercial users. After the product has been consumed, the container remains charged with some amount of the propellant. If the propellant is a flammable gas, the container is considered hazardous waste, even when the product is a water-based liquid.